Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional printing is an additive process in which one or more printheads eject successive layers of material on a substrate in different shapes. Typically, ejector heads, which are similar to printheads in document printers, include an array of ejectors that are coupled to a supply of material. Ejectors within a single ejector head can be coupled to different sources of material or each ejector head can be coupled to different sources of material to enable all of the ejectors in an ejector head to eject drops of the same material. Materials that become part of the object being produced are called build materials, while materials that are used to provide structural support for object formation, but are later removed from the object are known as support materials. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
A previously known three-dimensional object printing system 10 is shown in FIG. 11. In the view depicted in that figure, a platform 14, called a cart, includes surfaces 18 (FIG. 10) that slide upon track rails 22 to enable the cart to move in a process direction P between printing stations, such as the printing station 26 shown in FIG. 11. Alternatively, carts can include wheels configured to roll along tracks, or other types of acceptable mobility mechanisms. The rails 22 terminate at a position underneath the cart 14 as shown in FIG. 11. Printing station 26 includes four ejector heads 30 as shown in the figure, although fewer or more ejector heads can be used in a printing station. Once the cart 14 reaches the printing station 26, the cart 14 transitions to precision rails 38, which begin at the termination of the rails 22, to enable bearings 34 to roll upon precision rails 38. Precision rails 38 are cylindrical rail sections that are manufactured within tight tolerances to help ensure accurate placement and maneuvering of the cart 14 beneath the ejector heads 30. The rails 38 terminate past the printing station 26, as shown in FIG. 8, where another set of rails 22 (not shown) begin and then lead to the next printing station. Linear electrical motors are provided within housing 42 to interact with a magnet positioned with housing 46 connected to the lower surface of the cart 14, as described below, to propel the cart as the surfaces 18 slide along the track rails 22 and then, once the bearings 34 transition to the precision rails 38, maneuver the cart 14 on the precision rails. As the cart 14 moves on the rails 38 past the printing station 26, the printheads eject material onto the upper surface of the cart in synchronization with the motion of the cart. Additional motors (not shown) move the printing station 26 vertically with respect to the cart 14 and in an X-Y plane parallel to the upper surface of the cart as layers of material accumulate to form an object. Alternatively, a mechanism can be provided to move an upper surface of the cart 14 on which the object is being formed vertically and in the X-Y plane to enable the layers to form the object. Once the printing to be performed by a printing station is finished, the cart 14 is moved to another printing station for further part formation, layer curing or other processing.
An end view of the system 10 is shown in FIG. 10. That view depicts in more detail the surfaces 18 on which the cart 14 slides the track rails 22. Bearings 34 of the cart 14 are positioned on the precision rails 38 in an arrangement that facilitates accurate positioning of the build platen on the cart 14. Specifically, bearings 34 are positioned at a right angle to one another on one of the rails 38 to remove 4 degrees of freedom of the cart 14, while the other bearing 34 rests on the other rail 38 to remove one more degree of freedom. Linear motors within the housing 42 generate electromagnetic fields that interact with the magnet in housing 46 to move the cart 14 over an upper surface 50 of the housing 42. Gravity and magnetic attraction between the linear motors and the magnet hold the bearings 34 in contact with the rails 38.
Material ejected by the ejector heads 30 as well as other contaminants can accumulate and present a risk of damaging or impacting the accuracy of the ejector heads 30. For example, material within an ejector head can solidify to form a clog or partially obstruct the ejector head. Material from other ejector heads or other particulates can contaminate the ejector head. Similar risks are also present for other printing stations in the printing system 10.
Material that has accumulated on an ejector head or other printing station, or extraneous material from an improperly maintained ejector head can present other risks. When carts are not present underneath the ejector heads 30, errant drips of materials can fall from the ejector heads and produce undesired debris and contamination on the precision rails 38 and the housing 42. Also, air-borne contaminants in the environment, such as dust or other particulate matter, can fall and collect on the rails 38 and the housing 42. When these contaminants and debris are located at any interface between the bearings 34 and the rails 38, the linear velocity of the cart is disrupted and the quality of the printed object is affected. Similarly, when these materials are within the gap between the top surface 50 of the housing 42 and the magnet 46, the magnetic attraction can be affected and enable the cart to be less constrained. Additionally, the collection of material drops on top of the housing 42 can also affect the dissipation of heat from the motor and cause motion quality disturbances, impacting the performance and reliability of the motor. In order to produce three-dimensional objects with acceptable quality, the motion of the cart 14 beneath the ejector heads 30 needs to be precise. Therefore, improvements in three-dimensional printing systems that help prevent the contamination on the precision rails and motor housing that affects the accuracy of the placement and movement of the cart would be beneficial.
Regular maintenance to the ejector heads 30 and other printing stations is beneficial for maintaining accurate and efficient operation of the printing system 10, and for preventing material and other contaminants from accumulating on the precision rails and motor housing. Conventional three-dimensional printing system maintenance devices often require lengthy interruptions of the printing process, and include complex machinery beyond the components necessary for three-dimensional printing that can increase the machine footprint of the system. One example of a conventional maintenance device includes a maintenance cabinet separate from the printing system 10 that can be positioned next to a printing station to be maintained. The cabinet contains tools usable to maintain the printing station. In another example, an ejector head is moved to engage with a maintenance station configured to maintain the ejector head. Including a maintenance architecture that does not interrupt the printing process and that does not significantly increase the footprint of the printing system would be beneficial.